Flame-retarding material and process of making the same



Patented Nov. 16, 1948 FLAME-RETARDING MATERIAL AND PROCESS OF MAKING THE SAME l Jackson A. Woodruif, St. Davids, Pa., assignor to American Viscose Corporation, Wilmington, Del., a corporation of Delaware No Drawing. Application February 20, 1946,

Serial No. 649,131

1 This invention relates to cellulosic materials which are less flammable than normal cellulosic materials, and which may be exposed to water or aqueous media without loss of flame resistance, andto processes for producing the same.

Cellulosic materials are inflammable to substantially the, same extent as fibrous paper, and readily take fire when brought into contact with a flame. Moreover, the cellulosic materials support and propagate a flame so that it spreads rapidly to all parts of the cellulosic body from the point of initial contact. The so-called brushed rayons, for example, are highly inflammable, presenting the possibility of serious flre loss and personal damage from. the usual sources of accidental conflagration, which has prevented widespread use thereof, despite the fact that the brushed rayons have an especially soft, pleasing handle or feel.

' Tungsten has long been recognized as a particularly effective flameproofingagent for various types of textile materials, but has the disadvantage that it has to be applied to the material in the form of a. salt, such as the sodium salt, which is soluble in water. The flameproof quality imparted to the material is lost when the sodium tungstate is dissolved out of the material when the latter is brought into contact with water or aqueous media, as during laundering.

The presentinventionhas as an object the provision of cellulosic materials having improved re- 5 Claims. (Cl. 117-137) This invention accordingly comprises the several steps outlined, the relation of the steps with respect to each other, and the articles possessing the features, properties, and relation of the elements described herein.

The acid-soluble cyanamide-formaldehyde resin with which the cellulosic material which has been previously treated with an aqueous solution of sodium tu'ngstate is impregnated, may be obtained for example by reacting a mixture of substantially equimolecular proportions of cyan amide and formaldehyde in an aqueous solution having a pH between about 6 and 9 and at a temperature between about 70 C. to 100 C. After precipitation from the reaction mixture, washing and drying, the resin is obtained in the form of a soft, yellow powder which is insoluble in water and all organic solvents except definitely acid solvents. The solubility of the product in acids depends upon the conditions under which it is obtained. If the reaction product is precipitated from a, highly alkaline solution, it has a lower degree of solubility in acetic acid unless the reaction is carried out at higher temperatures. The solubility in acids is also affected by the temperatures at which the precipitate is dried, after washing thereof, the product being more readily dissolved sistance to flame by means of tungsten in the form of a water-insoluble or substantially water-inwith an aqueous dilution of an acid solution of an acid-soluble cyanamide formaldehyde resin. By a process of ion exchange, the sodium ions are replaced bythe cyanamide-formaldehyde reaction product, and the final article comprises a cellulosic body having firmly and substantially permanently incorporated therein and fixed thereto a water-insoluble complex of the cyanamideformaldehyde resin with tungsten.

by heating with a, relatively weak acid, such as formic or acetic acid, if the temperature is maintained at about 100 C. or lower, whereas boiling with the stronger mineral acids may be necessary in order to obtain a clear solution, if the precipitate is dried, after washing, at temperatures much higher than 100 C. For the present purposes, it is preferred to carry out the reaction of the cyanamide and formaldehyde, and to wash and .dry the precipitate obtained, under conditions such that the resin is soluble in the weaker acids, in order to avoid the use of the stronger acids, which may have a degrading effect upon the cellulose. However, since the treatment may be carried out at temperatures in the neighborhood of about 50 0., and it is suflicient to use aqueous dilutions of acid solutions of the resins of low concentration, of the order of about 2% of the resin dissolved in the acid, it is possible to utilize a resin prepared under such conditions that it is more readily dissolved by boiling with stronger acids of the type of hydrochloric acid, for instance, without noticeable ill efiect on the cellulose.

The following example illustrates the nature of the invention, but is not intended to limit the scope thereof.

aaeaaes Esamille A fabric formed from regenerated cellulose yarns was immersed in a aqueous solution of sodium tungstate for a period of one-half hour at 60 C. The fabric was removed from the bath,

extracted to remove excess treating liquid, and

thereafter immersed in an aqueous dilution of a 2% acetic acid solution of the precipitate obtained by reacting equimolecular proportions of cyanamide and formaldehyde in alkaline solution (pH '2) at 100 C., washing the precipitate, and drying it at'a temperature of 95. C. The treated fabric was then extracted and dried. The cellulosic article was brought into contact with the flame of a Bunsen burner at an angle of 45.

Charring occurred only at the area. covered by and immediately surrounding the flame, and there was no afterglow (flameless combustion). 'The treated fabric was found to be soft and pliable and to compare favorably in handle with normal rayon fabric. After being subjected to five washings with a one-half percent aqueous soap solution at about 40 C. each washing being of one-half'hour duration, the treated fabric was found to be substantially as flame-resistant as it was immediately after treatment with the sodium tungstate and acid-soluble resin and prior to the washing operations. The advantages of the invention reside particularly in the simplicity of the treating steps required, the possibility of using tungstate which is superior as a flame-proofing agent, and the fastness to washing which characterizes the treated cellulosic materials.

As mentioned in the foregoing example, when a cellulosic material is treated in accordance with this invention, flaming and charring occur only at the point of contact between the treated article and an independentflame applied thereto, and the'flame is not propagated along the material regardless of whether it is held at a 45 angle or horizontally. The materials are not caused to flame by contact with a non-incandescent body, such as an overheated electrical fixture or the like.

The invention is useful for imparting resistance to flaming and to the propagation of a flame to any cellulosic material, in any form, and especially to those materials which, in order to meet the rigid demands of the trade, are required to remain flame-resistant after repeated exposure to water, solutions of mild detergents or the like, and which should not show an afterglow after exposure to a direct flame.

The treatment may be applied to the cellulosic body in the raw state, in some processed state, or in manufactured form, particularly fabrics including broadcloths, muslin, cotton rep, sail, duck canvas, tarpaulin, window shades, curtain materials, mattress covers, upholstery fabrics, slip covers, tablecloths, draperies, awnings, rugs, blankets, etc., whether consisting of or comprising cellulose per se or cellulose regenerated from of cyanamide and formaldehyde in an aqueous,

medium having a pH of about 6 to 9, at temperatures between about 70 C. and 100 C.

2. A product comprising regenerated cellulose having incorporated therein and fixed thereto a cellulose with an aqueous solution of sodium 4 substantially water-insoluble complex of tungsten with the resin obtained by reactingsubstantially equlmolecular proportions of cyanamide and formaldehyde in an aqueous medium having a pH of about 6 to 9 at temperatures between about 70. C. and C.

3. The method of rendering cellulose flame resistant and capable of withstanding repeated wetting with water without substantial loss of flame resistance, which comprises treating the tungstate, removing excess treating liquid from the material, and thereafter treating the material with an aqueous dilution of an acid solution of the resin obtained by reacting substantially equimolecular proportions of cyanamide and formaldehyde in an aqueous medium having a pH of about 6 to 9, at a temperature between about 70 C. and 100 0., to thereby form on the cellulose a water insoluble complex of tungsten with the resin, and flx'the complex to the cellulose through the substantivity of the resin for cellulose, the complex being formed and fixed to the cellulose without benefit of curing.

4. The method of rendering cellulose flame resistant and capable of withstanding repeated wetting with water without substantial loss of flame resistance, which comprises treating the cellulose with an aqueous solution of sodium tungstate, removing excess treating liquid from the material, and thereafter treating the material with an aqueous dilution of an acetic acid solu-.

tion of the resin obtained by reacting substantially equimolecular proportions of cyanamide and formaldehyde in an aqueous medium having a pH of about 6 to 9, at a temperature between about 70 C. and 100 0., to thereby form on the cellulose a water insoluble complex of tungsten with the resin, and flx the complex to the cellulose through the substantivity of the resin for cellulose, the complex being formed and fixed to the cellulose without benefit of curing.

5. The method of rendering cellulose flame resistant and capable of withstanding repeated wetting with water without substantial loss of flame resistance, which comprises treating the cellulose with a 5% aqueous solution of sodium tungstate, removing excess treating liquid from the material, and thereafter treating the material with an aqueous dilution of a 2% acetic acid solution of the resin obtained by reacting substantially equimolecular proportions of cyanamide and formaldehyde in aqueous solution, at a pH of from 6 to 9, and at a temperature between about 70 C. and 100 C., to thereby form on the cellulose a water insoluble complex of tungsten with the resin, and fix the complex to the cellulose through the substantivity 'of the resin for cellulose, the complex being formed and fixed to the cellulose without benefit of curing.

JACKSON A. WOODRUFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,033,411 Carson Mar. 10, 1936 FOREIGN PATENTS Number Country Date 476,043 Great Britain Nov. 29, 1937 

